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In the embryo, root phloem develops independently in the upper hypocotyl, which lies between the embryonic root, and the cotyledon. [20] In an adult, the phloem originates, and grows outwards from, meristematic cells in the vascular cambium. Phloem is produced in phases. Primary phloem is laid down by the apical meristem and develops from the ...
Xylem and Phloem A stem is one of two main structural axes of a vascular plant , the other being the root . It supports leaves , flowers and fruits , transports water and dissolved substances between the roots and the shoots in the xylem and phloem , engages in photosynthesis, stores nutrients, and produces new living tissue. [ 1 ]
The phloem is the living portion of the vascular system of a plant, and serves to move sugars and photosynthate from source cells to sink cells. Phloem tissue is made of sieve elements and companion cells, and is surrounded by parenchyma cells. The sieve element cells work as the main player in transport of phloem sap.
Sieve elements are specialized cells that are important for the function of phloem, which is a highly organized tissue that transports organic compounds made during photosynthesis. Sieve elements are the major conducting cells in phloem. Conducting cells aid in transport of molecules especially for long-distance signaling.
Two kinds of vascular tissue occur in plants: xylem and phloem. Phloem and xylem are closely associated with one another and are typically located immediately adjacent to each other in the plant. The combination of one xylem and one phloem strand adjacent to each other is known as a vascular bundle. [14]
In vascular cambium, the primary phloem and xylem are produced by the apical meristem. After this initial development, secondary phloem and xylem are produced by the lateral meristem. The two are connected through a thin layer of parenchymal cells which are differentiated into the fascicular cambium.
The fascicular and interfascicular cambia thus join up to form a ring (in three dimensions, a tube) which separates the primary xylem and primary phloem, the cambium ring. The vascular cambium produces secondary xylem on the inside of the ring, and secondary phloem on the outside, pushing the primary xylem and phloem apart.
The phloem sugar is consumed by cellular respiration or converted into starch, which is insoluble and exerts no osmotic effect. With much of the sucrose having been removed, the water exits the phloem by osmosis or is drawn by transpiration into nearby xylem vessels, lowering the turgor pressure within the phloem. [ 4 ]